Assessment of patient-reported outcomes (PRO) such as health-related quality of life (HRQOL) and cancer-related symptoms has been shown to improve patient symptom monitoring, the identification of psychosocial problems, and patient-provider communication. Recently electronic PRO assessment (ePRO) methods have been developed. They allow for two features impossible to implement with conventional paper- based PROs: web-based administration, allowing for flexibility of assessment location and the use of real-time measurement methods, such as computer adaptive testing (CAT). While these features make ePRO assessment easier to implement in non-research clinical care, no published research to date has evaluated voluntary patient use of web-based ePRO systems, or evaluated the effect of assessment location (i.e., in- clinic or at-home) on ePRO results. This study aims to address these gaps in the literature by using an ePRO system with a breast cancer population studying how patient participation and behaviors vary by location. Breast cancer is the most common cancer among women in the United States, and side-effects of breast cancer treatment have been found to impact psychosocial and sexual function. Studies have reported that a significant proportion of cancer patients are unwilling to discuss sexual problems and psychosocial distress with their oncologists. Other studies have found that a social desirability bias exists for sensitive questions such as the self-reporting of risky health behaviors. Web-based ePRO administration presents a new opportunity to examine if a social desirability reporting bias is associated with certain questions among cancer patients by providing an alternative assessment location (at home), allowing patients to respond to sensitive questions that they may not feel comfortable to discussing in public. This study will evaluate the feasibility of voluntary, web-based PRO monitoring outside a clinical setting and if assessment location impacts patient self-report of sexual function and psychosocial distress. Breast cancer patients, under age 55 (n=130) will be followed longitudinally over their course of clinical care for 7 months. General and cancer-specific HRQOL domains will be assessed in two locations: in clinic (at baseline and 6 months) and at home (every month). Participation will be evaluated relative to patient demographics, clinical characteristics, and if the patients are currently in active treatment or within 5 years of completing treatment. At-home and in-clinic assessments for sexual function and psychosocial distress will be evaluated in the same week-long period to determine if significant mode effects exist by location. Findings from this study can be used to identify characteristics of users and non-users of web-based assessment methods in clinical oncology setting. This knowledge will help focus future efforts to include hard- to-reach segments of the patient population using technology-based assessment methods, and to expand the generalizability and use of web-based assessment methods in larger, diverse clinical settings.